1. Field of the Invention
The present invention relates to a reformer and a fuel cell system incorporating the same for generating electric power.
2. Discussion of the Related Art
As one form of reformers, there has been known a reformer which is described in Japanese unexamined, published patent application No. 2001-165431. As shown in FIG. 1 of the Japanese application, the reformer is provided with a raw fuel flow sensor 11 on a raw fuel supply passage 2 for supplying raw fuel to a reformer 1, and a feedback control is performed by a raw fuel flow controller FC1 regarding the opening degree of a raw fuel flow control valve 12. Further, an air flow sensor 13 is provided on an air supply passage 5 for supplying air to a reformer burner 4, and a feedback control is performed by an air flow controller FC2 regarding the opening degree of an air flow control valve 14. A target value for the flow of the raw fuel is restricted by a limiter 21 to come into a range of upper and lower limits which are set in dependence on an actual value of the air flow sensor 13, while a target value for the flow of air is restricted by another limiter 24 to come into another range of upper and lower limits which are set in dependence on the target value for the flow of the raw fuel. Accordingly, a large fluctuation in air-fuel ratio can be prevented in spite of the fluctuation in a load Z.
Further, another or second example has been known as one shown in Japanese unexamined, published patent application No. 2006-002991. As shown in FIG. 1 of the Japanese application, a reformer (hydrogen generator 1) is provided with a plurality of temperature detecting means 26 for detecting the temperatures of respective parts of a combustion section 18 which burns city gas, LPG, offgas (non-reacted hydrogen gas) exhausted from a fuel cell, or a gaseous body consisting of a mixture of city gas or LPG and offgas, and a control section 22 responsive to data from the temperature detecting means 26 for judging the combustion state of the combustion section 18 and for controlling blower means 21.
Further, a third example has been known as one shown in Japanese unexamined, published patent application No. 2005-257190. As shown in FIG. 1 of the Japanese application, a reformer (hydrogen generator 1) is provided with a pressure detecting means 26 for detecting the pressure on a downstream side of a combustion section 18 which burns city gas, LPG, offgas exhausted from a fuel cell or a mixture gas thereof, and a control section 22 responsive to data from the pressure detecting means 26 for judging the combustion state of the combustion section 18 and for controlling blower means 21.
Additionally, a fourth example has been known as one shown in Japanese unexamined, published patent application No. 2005-090855. As shown in FIG. 1 of the Japanese application, a reformer (hydrogen generator 1) is provided with a distributor 9 for ejecting fuel, an air blower section 10 for supplying air 11 to the fuel, pressure detecting means 22 for the fuel supplied to the distributor 9, and a control section 21 responsive to data from the pressure detecting means 22 for judging the combustion state.
However, in the reformer described in the first mentioned Japanese application, when the air-fuel ratio is shifted to the lower side due to detection errors in the raw fuel flow sensor 11 or the air flow sensor 13, it is likely to occur that the combustion section goes out, and thus, the combustion is apt to become unstable. When the air-fuel ratio is shifted to the higher side, on the contrary, the heat loss becomes larger at the combustion section because of much volume of air which does not contribute to combustion, and the efficiency is apt to go down. Further, the use of the flow sensors which are generally more expensive than temperature sensors may cause the device to rise in cost.
The reformers described in the second through fourth Japanese applications are configured respectively to perform the combustion state judgment of the combustion section 18 and the control of the blower means 21 in receipt of the data from the plurality of temperature detecting means 26 for detecting the temperatures of respective parts of the combustion section 18; to perform the combustion state judgment of the combustion section 18 and the control of the blower means 21 in receipt of the data from the pressure detecting means 26 for detecting the pressure on the downstream side of the combustion section 18; and to perform the judgment of the combustion state in receipt of the data from the pressure detecting means 22 for the fuel supplied to the distributor 9. However, because the combustion state in each of the reformers is judged in dependence on the data from the various detecting means, there is a risk that the combustion may be erroneously judged due to detection errors in the detecting means.